1. Field of the Invention
The present invention relates to a semiconductor device having a plurality of interconnection layers and to a production method for the semiconductor device.
2. Description of Related Art
Semiconductor devices generally include a semiconductor substrate, a functional device provided in a surface of the semiconductor substrate, and a multi-level interconnection structure provided on the semiconductor substrate. The multi-level interconnection structure typically includes a plurality of interconnection layers stacked with the intervention of interlevel insulation films, and connection between the interconnection layers is achieved through contact holes formed in the interlevel insulating films.
Aluminum is conventionally employed as an interconnection material, but has a limitation in reduction of the resistance of the interconnection. As the sectional area of the interconnection is reduced with microminiaturization of the semiconductor device, a problem associated with the resistance of the interconnection arises. As a result, particularly, there is a demand for reduction of the resistances of a ground line and a power line.
In this connection, the inventor of the present invention, for example, has proposed in U.S. 2002-132392A1 that a gold layer is employed as an uppermost interconnection layer for the reduction of the resistance of the interconnection.
In this prior art, a barrier layer of a titanium thin film is disposed between an aluminum interconnection layer and the uppermost gold interconnection layer electrically connected to each other through a contact hole, so that migration of aluminum is prevented by the barrier layer.
However, gold is a highly diffusible material. Where the semiconductor device is allowed to stand at a high temperature for a long period of time (e.g., at 400° C. for 30 minutes to 1 hour) in an alloying process, for example, gold easily diffuses into the aluminum interconnection layer.
In practice, the titanium thin film has virtually no function as the barrier layer, but merely functions as an adhesive layer to contribute to the bonding between the interlevel insulation film and the gold layer and the bonding between the aluminum interconnection layer and the gold layer.
Besides the titanium thin film, a TiW thin film is conceivably usable as the barrier layer. However, like the titanium thin film, the TiW film has virtually no function for prevention of mutual diffusion between the gold layer and the aluminum interconnection layer, but merely functions as an adhesive layer.
Although electrically conductive materials having a barrier effect should be employed for the formation of the barrier layer, such materials have difficulty in forming a barrier layer having a uniform thickness. More specifically, the barrier layer is liable to have a reduced thickness on the bottom (especially, at a corner of the bottom) of the contact hole formed in the interlevel insulation film, resulting in poor coverage. Therefore, the barrier layer fails to provide a sufficient barrier effect in a heat treatment at a high temperature.